Dresden 2011 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 25: Colloids and Complex Liquids I - Structure

CPP 25.5: Vortrag

Mittwoch, 16. März 2011, 11:45–12:00, ZEU 222

(contribution withdrawn) Binary mixture of charged colloidal spheres with a spindle-type phase diagram — •Janina Marquis, Nina Lorenz, and Thomas Palberg — Institute of Physics, University of Mainz, Germany

Colloidal suspensions are an important model system for solid state physics and statistical mechanics. Their phase behaviour and crystallization kinetics are conveniently accessible via optical methods like light scattering and microscopy.

We have studied the phase behaviour and other properties of a deionized binary mixture of charged colloidal spheres with a size ratio of Γ =a_s/a_l=0.90 and a charge ratio of Λ =Z_s/Z_l=0.8 as a function of composition. Here the screened Coulomb interaction is increased by increasing the total particle number density (sulphate stabilized Polystyrene-Poly-n-Butylacrylamide copolymer particles: diameter: 2a_s=118nm, 2a_l=131nm, effective charges from elasticity: Z_s^eff=401 ± 20, Z_l^eff=499 ± 21). Both pure samples and the mixtures crystallize in a bcc structure with the latter forming random substitutional crystals. The liquidus as a function of composition stays roughly horizontal, whereas the solidus curves symmetrical to higher number densities and the coexistence region is widened to a horizontally oriented spindle. Similarities and differences to other charged sphere mixtures are discussed [1, 2].

[1] N. J. Lorenz et al.: J. Phys.: Condens. Matter 21, 464116 (2009)

[2] N. J. Lorenz, T. Palberg,: J. Chem. Phys. 133 104501 (2010)